Kelvin to Celsius: K to °C Converter
Convert Kelvin to Celsius (or any temperature scale) instantly. Subtract 273.15 from Kelvin to get Celsius. Used in science, photography (color temperature), and engineering. Enter a Kelvin value below and see Celsius and Fahrenheit equivalents update in real time.
°F = (0 × 9/5) + 32 = 32°F
Kelvin to Celsius reference table
| Kelvin | Celsius | Note |
|---|---|---|
| 0 K | -273.15°C | Absolute zero |
| 100 K | -173.15°C | Liquid oxygen |
| 200 K | -73.15°C | Mars night |
| 273.15 K | 0°C | Water freezes |
| 293.15 K | 20°C | Room temperature |
| 310.15 K | 37°C | Body temperature |
| 373.15 K | 100°C | Water boils |
| 500 K | 226.85°C | Hot oven |
| 1000 K | 726.85°C | Red-hot metal |
| 3200 K | 2,926.85°C | Halogen lamp light |
| 5500 K | 5,226.85°C | Daylight white balance |
About Kelvin to Celsius
The relationship
Kelvin and Celsius share the same degree size. A change of 1 K equals a change of 1°C. They differ only in where zero is. Celsius puts zero at the freezing point of water. Kelvin puts zero at absolute zero, the theoretical lowest possible temperature. To convert from Kelvin to Celsius, subtract 273.15. To convert the other way, add 273.15.
Absolute zero in context
At 0 K, all molecular motion would stop. In practice, no system can be cooled exactly to absolute zero (the third law of thermodynamics ensures this). The closest temperatures achieved in laboratories are in the nanokelvin range (billionths of a Kelvin above absolute zero), using laser cooling and magnetic trapping techniques.
Temperatures in nature
Cosmic microwave background (the residual heat from the Big Bang): 2.725 K. Coldest measured location in the universe (the Boomerang Nebula): about 1 K. Liquid nitrogen: 77 K (-196°C). Triple point of water (used to define Celsius): 273.16 K = 0.01°C. Sun's core: 15 million K. Particle accelerator collisions briefly reach trillions of Kelvin.
Why scientists prefer Kelvin
Most physical laws are simpler in Kelvin because absolute temperature has a natural starting point. The ideal gas law PV=nRT requires Kelvin. Thermodynamic efficiency uses ratios of absolute temperatures. Stefan-Boltzmann radiation law uses absolute temperature to the fourth power. Wien's displacement law (used in astronomy and photography color temperature) uses absolute temperature directly.
Subtract 273.15 from Kelvin to get Celsius. So 300 K = 26.85°C, 273.15 K = 0°C, 373.15 K = 100°C. The two scales use the same degree size; they only differ in where zero is.
Add 273.15 to Celsius. So 20°C = 293.15 K, 100°C = 373.15 K. The reverse of the Kelvin-to-Celsius operation.
300 K = 26.85°C. This is slightly above typical room temperature (20°C / 293 K). Standard "STP" (Standard Temperature and Pressure) in some scientific contexts uses 298.15 K = 25°C.
0 K = -273.15°C. This is absolute zero, the theoretical lowest possible temperature where all molecular motion stops. It cannot be reached in practice, though laboratories have come within billionths of a degree.
Many physical formulas require absolute temperature. The ideal gas law (PV = nRT) uses Kelvin natively. Thermodynamic efficiency calculations use absolute temperature ratios. Blackbody radiation laws (Stefan-Boltzmann, Wien) use Kelvin. Using Celsius would require awkward offsets in these equations.
Normal body temperature (37°C) = 310.15 K. Room temperature (20°C) = 293.15 K. Refrigerator (4°C) = 277.15 K. Freezer (-18°C) = 255.15 K.
Exact. The offset of 273.15 is the SI-defined relationship between Celsius and Kelvin. The calculator shows 6 significant figures, more than any practical temperature measurement uses.
No. Kelvin is written without a degree symbol: 300 K, not 300°K. This emphasizes that Kelvin is an absolute scale. Celsius and Fahrenheit use degree symbols because they are relative scales with arbitrary zero points.
In the empty space between stars, the cosmic microwave background radiation gives a temperature of about 2.725 K (-270.4°C). Specific regions of space can be much colder or hotter; the interior of the Sun reaches 15 million K, while the surface of Mars at night drops below 150 K (-123°C).
Because it is the only temperature scale tied directly to a fundamental physical reference (absolute zero) rather than to arbitrary reference points like water's phase transitions. The Kelvin definition was redefined in 2019 to be based on the Boltzmann constant, making it independent of any specific substance.
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